Professor Jiabao Yi

Materials with specific magnetic properties are required for spin generation, manipulation, and detection for spintronics applications. Transition metal (TM) doped semiconductors and oxides, which were expected to meet this requirement, are facing problems due to formation of secondary phases and clusters. To overcome this problem, researchers have gone beyond traditional magnetic TM doped semiconductors and oxides and have started looking for alternative dopants. Some breakthroughs have been made recently. In this article, we review progress made along this direction and discuss possible origins of the unexpected ferromagnetism observed in materials without magnetic elements. We focus on dilute magnetic semiconductors and oxides obtained by doping with elements with a full d-shell or 2p light elements. It has been demonstrated that room temperature ferromagnetism can be achieved in such systems.

Plastic wastes were catalytically transformed into different structured carbons as effective catalysts for peroxymonosulfate activation to degrade organic pollutants in water and the catalytic conversion mechanism was comprehensively investigated. A salt template-based carbonization approach was successfully developed to catalytically converting high-density polyethylene (HDPE) into diverse carbon materials, such as core-shell carbon composites, nanosheets, and their hybrids. The morphology and proportions of structure defective carbon were found to be controlled by a NiCl2 to HDPE ratio. Carbon nanosheets performed excellent catalytic efficiency in peroxymonosulfate activation toward phenol oxidation, due to a high content of reactive defects via a nonradical electron-transfer mechanism. More importantly, deliberate experiment design and kinetic analyses were employed to illustrate the artifact of radical scavengers (e.g., ethanol) in mechanistic investigation for nonradical/radical reaction. This work provides an upcycle approach for waste plastics into carbocatalysts and new insight to the conversion process and advanced water purification.

Thin film epitaxy is essential for state-of-the-art semiconductor applications. The combination of different substrates and deposition methods leads to various crystallographic orientation relationships between thin films and substrates, which have a decisive impact on thin film performance. By utilizing pulsed laser deposition, we discovered a very high-index (7 1 ¯ 4) ¿oriented NiO thin film when deposited on r-plane (10 1 ¯ 2) sapphire substrates. The in-plane epitaxial relations are [13 1 ¯] NiO||[1 2 ¯ 10] Sapphire and [1 ¯ 12] NiO||[10 11 ¯] Sapphire , and the lattice mismatch is 3.2% and 0.4% along two directions, respectively. Exchange bias studies by the deposition of Co on NiO (111) and NiO (7 1 ¯ 4) show different behaviors, which may be associated with the spin density and alignment on the surface. Graphical abstract: [Figure not available: see fulltext.].

Metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs) are constituting two new classes of highly crystalline advanced permeable materials that have purchased significant courtesy due to their incredible characteristic such as large surface area, highly ordered pores/channels, and controllable crystalline structure. However, the main hurdles to their various applications in photocatalytic activity and novel energy storage/conversion devices are their low structural stability and electrical conductivities. Therefore, substantial research has been directed to maximize their advantages and mitigate the shortcomings of these fascinating materials. In this review article, we first introduced the background and brief timeline of COF/MOF development and notable milestones followed by a systematic overview of the different synthetic procedures and recent achievements and milestones of their applications in CO2 reduction, hydrogen production, lithium-ion batteries (LIBs), and supercapacitors (SCs). Finally, the challenges and future perspectives on further developing high-performance COF/MOF materials for photocatalysis and electrochemical energy storage application are discussed.

Starting from sterically encumbered 2,6-di-tert-butylphenyl phosphate (dtbppH2) and co-ligand 3,5-dimethyl pyrazole (dmpz), it is possible to isolate either mono-, di- or tetranuclear copper phosphates by varying the copper source and making attendant changes in the reaction conditions. For example, reaction of copper nitrate with dtbppH2 and dmpz at 60 °C leads to the isolation of the mononuclear copper phosphate [Cu(dtbppH)2(dmpz)(MeOH)2] (1) as the only product. However, the use of copper acetate in place of copper nitrate and conducting the reaction at the room temperature leads to the formation of both dinuclear [Cu(dtbpp)(dmpz)2]2 (2) and tetranuclear [Cu2(dtbpp)(dmpz)2(OAc)(MeO)]2 (3) from the same reaction mixture. Compounds 2 and 3 could be isolated in pure form through fractional crystallization. Copper phosphates 1¿3 have been characterized by both analytical and spectroscopic methods including EPR and magnetic measurements. The molecular structures of all three compounds were established through single crystal diffraction studies. Dc magnetic measurements indicate antiferromagnetic interactions between the metal centres in all the compounds.

The rapid growth in electronic and portable devices demands safe, durable, light weight, low cost, high energy, and power density electrode materials for rechargeable batteries. In this context, biomass-based materials and their hybrids are extensively used for energy generation research, which is primarily due to their properties such as large specific surface area, fast ion/electron kinetics, restricted volume expansion, and restrained shuttle effect. In this review, the key advancements in the preparation of biomass derived porous carbons using different synthesis strategies and their modifications with species such as heteroatoms, metal oxides, metal sulfides, silicon, and other carbon forms are discussed. The electrochemical performances of these materials and the ion storage mechanisms in different batteries including lithium-ion, lithium¿sulfur, sodium-ion, and potassium-ion batteries are discussed. Special attention will be paid to the challenges in using porous biomass-derived carbons and the current strategies employed for maximizing the specific capacity and lifetime for battery applications. Finally, the drawbacks in current technology and endeavors for the future research and development in the field to catapult the performances of the biomass derived materials in order to equip them to meet the demands of commercialization are highlighted.

With the increase of energy crisis and greenhouse effect, the development of new photocatalytic systems with efficient solar-driven fuels/chemicals production is of great practical and scientific importance. In this scenario, single atom photocatalytic (SAP) systems are considered a significant breakthrough in the development of heterogeneous photocatalysis due to their superior catalytic efficiency, large surface area, and high atomic utilization. SAPs are consisting of isolated single atoms (SAs) distributed on/or coordinated with surface atoms of a suitable support. The anchoring of SAs on 2D substrates endows the developed SAPs with excellent properties, including high loading, uniform coordination, high light harvesting capability, and enhanced photocatalytic activities. Recently, many 2D substrates, including carbon materials, MXenes, and transition metal chalcogenides, have been used to anchor metal SAs for different photocatalytic applications. This review systematically discusses SAPs and the confining of metal SAs on 2D supports. Moreover, this review highlights the recent advances of SAPs for energy conversion, the existing challenges, and future perspectives. We expect that this review will offer some ideas for the future discovery of novel photocatalytic systems.

Due to its high energy density and non-polluting combustion, hydrogen has emerged as one of the most promising candidates for meeting future energy demands and realising a C-free world. However, the wider application of hydrogen is restricted by issues related to the generation, storage, and utilisation. Hydrogen production using steam reforming leads to CO2 emissions, storage of hydrogen requires extreme conditions, and utilisation of hydrogen needs to be highly efficient. Solid materials, can play significant roles in hydrogen sector as these materials are appropriate for the effective generation, storage, and utilisation of hydrogen. Their physical, chemical, thermal, and electronic properties can be easily manipulated to enhance their efficiencies in all three areas. In this review, various materials are described for the photocatalytic, electrocatalytic, and photoelectrocatalytic production, physisorption- and chemisorption-based storage, and utilisation of hydrogen in fuel cells; moreover, chemical and ammonia syntheses and steelmaking have been comprehensively discussed. Detailed insights and relevant comparisons are provided to demonstrate the efficacies of the abovementioned materials in the hydrogen sector. This broad overview of materials development will promote the hydrogen economy and inspire researchers and policymakers to appreciate the roles of materials and invest more in their research and development.

Infrared (IR) detectors have important applications in numerous civil and military sectors. HgCdTe is one of the most important materials for IR detector manufacture. This review systematically discusses the progress of HgCdTe materials grown via molecular-beam epitaxy (MBE) for IR detection in terms of material physics, structure design, and fabrication. The material physics of HgCdTe includes crystal information, band structure, and electrical and optical properties. The characterization methods of the As-grown HgCdTe materials are also summarized. Then, four design structures of HgCdTe for IR detectors, with multilayer, superlattice, double-layer heterojunction, and barrier properties, which significantly improve the device performance, are discussed. The third section summarizes the studies on HgCdTe MBE-grown on different substrates, including CdZnTe, Si, and GaSb, in recent decades. This review discusses the factors influencing the growth of the HgCdTe film and their relationships and optimal conditions. Finally, we present the prospects and challenges associated with the fabrication and applications of HgCdTe materials for IR detectors.

The accumulation of waste plastics has caused serious environmental issues due to their unbiodegradable nature and hazardous additives. Converting waste plastics to different carbon nanomaterials (CNMs) is a promising approach to minimize plastic pollution and realize advanced manufacturing of CNMs. The reported plastic-derived carbons include carbon filaments (i.e. carbon nanotubes and carbon nanofibers), graphene, carbon nanosheets, carbon sphere, and porous carbon. In this review, we present the influences of different intrinsic structures of plastics on the pyrolysis intermediates. We also reveal that non-charring plastics are prone to being pyrolyzed into light hydrocarbons while charring plastics are prone to being pyrolyzed into aromatics. Subsequently, light hydrocarbons favor to form graphite while aromatics are inclined to form amorphous carbon during the carbon formation process. In addition, the conversion tendency of different plastics into various morphologies of carbon is concluded. We also discuss other impact factors during the transformation process, including catalysts, temperature, processing duration and templates, and reveal how to obtain different morphological CNMs from plastics. Finally, current technology limitations and perspectives are presented to provide future research directions in effective plastic conversion and advanced CNM synthesis.

Graphene, sp2-hybridized miracle material of 21st century possesses extra-ordinary physico-chemical properties and hence inspires several salient frontline applications. Lack of magnetic ordering limits its dream spintronic chips applications. Phosphorus and sulfur being large and electron-rich atoms, if adequately doped to graphene, will enable carrier injection (worth for electronic chips) and net spin-polarized electrons (worth for spintronic chips) in it. However, in-plane (preferentially) ultra-doping of graphene by phosphorus and sulfur is extremely challenging by conventional techniques. We report microwave doping of graphene by phosphorus and sulfur atoms up to record doping level of 15 and 12.5 % respectively which render graphene room temperature ferromagnetism with a saturation magnetization as high as 0.13 emu/g and 0.15 emu/g for phosphorus and sulfur doping ¿respectively¿. Spin-polarized DFT band structure calculations suggest vivid spin asymmetry caused by doping which supports our experimental findings of primarily graphitic doped samples. Microwave doping of graphene by phosphorus and sulfur brings in dramatic changes in its magnetic behaviour and thus the present research establishes it as a novel doping strategy with excellent efficiency, scalability, and reproducibility, and will inspire new generations of graphene-based spintronic chips.

Metal-semiconductor diodes constructed from two-dimensional (2D) van der Waals heterostructures show excellent gate electrostatics and a large built-in electric field at the tunnel junction, which can be exploited to make highly sensitive photodetector. Here we demonstrate a metal-semiconductor photodiode constructed by the monolayer graphene (Gr) on a few-layer black phosphorus (BP). Due to the presence of a built-in potential barrier (~0.09 ± 0.03 eV) at the Gr-BP interface, the photoresponsivity of the Gr-BP device is enhanced by a factor of 672%, and the external quantum efficiency (EQE) increases to 648% from 84% of the bare BP. Electrostatic gating allows the BP channel to be switched between p-type and n-type conduction. We further demonstrate that excitation laser power can be used to control the current polarity of the Gr-BP device due to photon-induced doping. The versatility of the Gr-BP junctions in terms of electrostatic bias-induced or light-induced switching of current polarity is potentially useful for making dynamically reconfigurable digital circuits.

We demonstrate a synthesis of copper nanoparticles decorated over nitrogen-doped mesoporous carbon with different N and Cu contents which exhibit conducting, redox, basic, adsorption, and excellent textural properties. These materials are prepared through a nanotemplating approach by simultaneously encapsulating sucrose, guanidine hydrochloride, and Cu(NO3)2 into the porous channels of mesoporous SBA-15 at a low carbonization temperature of 600 °C. The prepared materials exhibit an ordered mesoporous carbon framework with bimodal pores, decorated with nitrogen and Cu functionalities on the surface of the pores and in the wall structure. The presence of nitrogen functionalities in the porous carbon matrix not only helps to reduce the Cu ions but also stabilizes the nanoparticles and offers redox sites, which are beneficial for adsorption and electrochemical applications. The optimized sample exhibits the highest adsorption capacity of different gases such as CO2 ¿ 22.5 mmol/g at 273 K, H2 -13.5 mmol/g at 77 K at 30 bar and CH4 - 5 mmol/g at 298 K and 50 bar. We also demonstrate that the prepared material shows a high selectivity of adsorption towards CO2 in a mixture of CO2/H2 and CO2/CH4 and it also registers a high supercapacitance of 209 F g-1 at a current density of 1 A g-1 with excellent cyclic stability.

The coupling of optical and electronic degrees of freedom together with quantum confinement in low-dimensional electron systems is particularly interesting for achieving exotic functionalities in strongly correlated oxide electronics. Recently, high room-temperature mobility has been achieved for a large bandgap transparent oxide ¿ BaSnO3 upon extrinsic La or Sb doping, which has excited significant research attention. In this work, we report the realization of a two-dimensional electron gas (2DEG) on the surface of transparent BaSnO3 via oxygen vacancy creation, which exhibits a high carrier density of ~7.72 × 1014 cm-2 and a high room-temperature mobility of ~18 cm2·V-1·s-1. Such a 2DEG is rather sensitive to strain and a less than 0.1% in-plane biaxial compressive strain leads to a giant resistance enhancement of ~350% (more than 540 kO/¿) at room temperature. Thus, this work creates a new path to exploring the physics of low-dimensional oxide electronics and devices applicable at room temperature.

In order to overcome the current energy and environment crisis caused by fossil fuels depletion and greenhouse gas emission, it is indispensable to introduce new, eco-friendly, high-performance materials into energy conversion and storage applications. 2D transition metal oxides (TMOs) are regarded as the promising candidates due to their excellent electrochemical properties. However, their innate poor electronic conductivity greatly restricts their applications in energy conversion and storage. This review discusses and summarizes the developed strategies to overcome the limitation through surface modification including defect engineering, heteroatom incorporation and interlayer doping, as well as hybridization with conductive materials. In addition, a detailed summary of their synthesis and applications in supercapacitors, lithium ion batteries and electrocatalysis is included. Finally, future prospective such as opportunities and challenges is discussed for the successful implementation of 2D TMOs in the field of energy applications.

Copper iodide (CuI) is a promising p-type wide bandgap semiconductor for optoelectronic and thermoelectric applications. Its p-type conductivity is due to the existence of native defect copper vacancy (VCu). We report the effect of native defects on microstructural, optical, and thermoelectric properties of ion beam sputtered CuI films via vacuum annealing. X-ray diffraction results showed that the CuI film is a ¿-phase with zinc blende crystal structure, further confirmed by Raman spectroscopy analysis. Cu-rich region was observed in vacuum-annealed films by cross-section transmission electron microscopy and element mapping, while as-deposited film is very uniform. As-deposited film exhibited an electrical conductivity s = 22.9 S cm-1, hole density p = 3.3 × 1019 cm-3, hole mobility µp = 4.3 cm2 V-1 s-1, and the Seebeck coefficient a = 244.9 µV K-1 which yielded a power factor of a2s = 137.8 µW m-1 K-2, whereas vacuum annealing led to the large increase in Seebeck coefficient a = 561.8 µV K-1 and a strongly increased power factor, a2s = 443.5 µW m-1 K-2 along with the slightly decreased conductivity, s = 14.0 S cm-1 when the film was annealed at 100 °C. The increase in Seebeck coefficient is attributed to the decrease in hole density along with energy-dependent scattering of charge carriers at the grain boundaries between CuI and Cu-rich region. The decreased hole density is due to the formation of less VCu in high vacuum annealing condition. In addition, the film exhibited 60¿85% transmission in the visible region. The results demonstrated that by a simple vacuum annealing, a high performance transparent thermoelectric material could be achieved, which provides a simple strategy for improving the properties of thermoelectric materials. Graphical abstract: [Figure not available: see fulltext.].

In this investigation, a hybrid of metal sulfide and carbon nitride (CN) is synthesized by in-situ chemical conversion between metallic species and a single precursor of carbon, nitrogen and sulfur elements through a strong p-d conjugation approach. It is observed that the local chemical alteration in the vicinity of N atom in the CN template triggers the formation of a highly p-conjugated CN system and efficient p-d hybridization at heterointerface. This is accelerated by partial substitution of the Fe atom for Mn ions in the MnS phase which significantly enhances the battery performance, delivering 2031 mA h g-1 after 500 cycles with inverse capacity growth. Via systematic in-depth characterizations, it is found that the gradual increase of Li-ion diffusion coefficients and charge transfer kinetics for repeated cycling is ascribed to the highly dispersed and uniform particles that are confined within the CN template through a strong p-d hybridization.

One of the most attractive features of magnetic ferrite nanoparticles (MFNPs) in biomedical application is that they can mediate external magnetic field to produce local magnetic field, magnetic thermal and magnetic force effects. These generated effects can later be utilized in the diagnosis and treatment of various diseases. The application performance is mainly determined by the nano-magnetism of MFNPs. Therefore, by modulating the magnetic properties, the improved magnetic resonance (MR) signals, magnetothermal, and magnetomechanical effects of the MFNPs can be achieved. In this review, we summarize the strategies used in the engineering of MFNPs to enhance MR imaging sensitivity and magnetic thermal conversion efficiencies. We will also discuss the detailed magnetoresponsive mechanism arising from the critical magnetic properties of MFNPs. Furthermore, we will highlight the recent progresses of the engineered MFNPs in biomedical applications, with emphasis in MR signal amplification, magnetothermal, and magnetomechanical response in biomedical applications.

The present study reports room-temperature ferromagnetic behaviors in three-dimensional (3D)- aligned thiol-capped single-crystalline ZnO nanowire (NW) and nanotube (NT) arrays as well as polycrystalline ZnO NT arrays. Besides the observation of height-dependent saturation magnetization, a much higher Ms of 166 µemu cm -2 has been found in NTs compared to NWs (36 µemu cm -2) due to larger surface area in ZnO NTs, indicating morphology-dependent magnetic properties in ZnO NW/NT systems. Density functional calculations have revealed that the origin of ferromagnetism is mainly attributed to spin-polarized 3p electrons in S sites and, therefore, has a strong correlation with Zn-S bond anisotropy. The preferential magnetization direction of both single-crystalline NTs and NWs lies perpendicular to the tube/wire axis due to the aligned high anisotropy orientation of the Zn-S bonds on the lateral (100) face of ZnO NWs and NTs. Polycrystalline ZnO NTs, however, exhibit a preferential magnetization direction parallel to the tube axis which is ascribed to shape anisotropy dominating the magnetic response. Our results demonstrate the interplay of morphology, dimensions, and crystallinity on spin alignment and magnetic anisotropy in a 3D semiconductor nanosystem with interfacial magnetism. © 2010 American Chemical Society.

In this work, the substrate grain size effect on the deposition of Ni79Fe21 film by electroplating has been studied. The morphology, surface roughness, particle size and magnetic properties of the deposited films are investigated in detail. The investigation shows that the grain size of the deposited films scales with the increase of the substrate grain size. It has shown that the surface roughness of the substrate is of importance. The smoother the substrate surface, the smaller the surface roughness and material coercivity of the deposited Ni79Fe21 film. This study indicates that the smoothness and uniformity of the substrate surface are important parameters to be taken into account during electroplating. Under such consideration, Ni81Fe19/Cu composite wire has been deposited by sputtering a layer of Cu on the Cu substrate surface to improve Cu wire surface smoothness and uniformity. It is found that with the sputtered Cu layer, the GMI effect of the deposited Ni81Fe19/Cu composite wire has been significantly increased. © 2006 Elsevier B.V. All rights reserved.

One dimensional (ID) oxide nanostructures such as nanowires (NWs) are strategically important for both basic science and technological applications. These emerging nanomaterials have demonstrated superb physical properties. In particular, nanowires of wide band gap semiconductors are promising as building blocks in optoelectronic and transparent electronics, and doping with transition metals can result in ferromagnetism. Here we report on the synthesis of ZnO, In2O3 nanostructures and their doped counterparts. Their physical properties have been measured systematically and they show great potential in electronic and spintronic applications. ©2010 IEEE.

The continued down-scaling of complementary metal-oxide-semiconductor (CMOS) devices requires replacement of the conventional Si dioxide or oxynitride dielectric by alternative high-k materials immediately. For long term consideration, electron devices may be replaced by spintronic devices which make use of both charge and spin, two fundamental properties of electron. However, to realize these, many materials issues to be addressed. Materials design based on computational methods is playing an increasingly important role in today's materials science and engineering research. Among the various approaches, the first-principles electronic structure method based on density functional theory (DFT) is ideal for designing new materials because such methods do not require experimental inputs and prior knowledge on the materials. We have been using first-principles method to study properties of materials for future advanced technologies and to design new materials. Some of our recent works are discussed. © 2010 IEEE.

Single- and poly-crystalline metal and alloy nanowires have been successfully fabricated into anodic aluminum oxide (AAO) template by electroplating. The single crystal-crystalline Ni and Co nanowires have been found at relatively high current density. Moreover, Ni and Co nanowires have a preferred orientation along the [2 2 0] and [1 0 0] direction, respectively. Single-crystal Ni nanowires showed coercivity 1 kOe with remanent 0.997, while Co nanowires showed coercivity 1.3 kOe and remanent 0.797. The different structures of NiCo nanowires have been obtained by varying the deposition conditions and current densities. The unique bamboo-like nanostructure was found in the product. Bamboo-like structure is achieved when the composition of 15 at% Co. The investigation of the mechanisms shows the special structures are related to the different diffusion rates of Ni and Co on the surface of AAO template. The work shows the possibility to control the sub-nanostructures in nanowires. © 2009 World Scientific Publishing Company.

We have fabricated metal/alumina hybrid materials by electrodepositon of metal nanowires into nanopores of anodic aluminum oxide templates. Single crystalline Ni and Co nanowires have been successfully fabricated. Structural characterization (XRD and HRTEM) shows that the single crystalline Ni nanowire has a preferred orientation along (220) direction. The preferred orientation of Co nanowire is along (100). These single crystalline Ni and Co nanowires have exhibited excellent magnetic properties. Their alloy nanowires have exhibited a large shift in hysteresis, probably due to the surface oxidation and exchange bias effect.

Co/CoO hybrid films are prepared by annealing Co films with various ratio of oxygen of O2/Ar mixture. The nanocomposite film shows a relatively large exchange bias (5.32 kOe) and coercivity (HC-: 6.17 kOe) taken at 80 K when formed by post annealing at 473 K under 3% O2 for 1h. Both are much larger than that of Co/CoO nanocomposite by reactive sputtering with an oxygen partial pressure. Investigation shows that the formation of interface by post annealing is of importance for the large exchange bias and enhanced coercivity. The surface CoO, grain size of CoO and composition may also contribute to magnetic properties of the post annealing film.